One common method for printing images on a receiver member is referred to as electrophotography. In this method, an electrostatic image is formed on a dielectric member by uniformly charging the dielectric member and then discharging selected areas of the uniform charge to yield an image-wise electrostatic charge pattern. Such discharge is typically accomplished by exposing the uniformly charged dielectric member to actinic radiation provided by selectively activating particular light sources in an LED array or a laser device directed at the dielectric member. After the image-wise charge pattern is formed, the pigmented (or in some instances, non-pigmented) marking particles (generally referred to as toner particles) are given a charge, substantially opposite the charge pattern on the dielectric member and brought into the vicinity of the dielectric member so as to be attracted to the image-wise charge pattern to develop such pattern into a visible image.
Thereafter, a suitable receiver member (e.g., cut sheet of plain bond paper) is brought into juxtaposition with the toner particles thus developed in accordance with the image-wise charge pattern on the dielectric member, either directly or via an intermediate transfer member such as a transfer roller or a transfer belt. A suitable electric field is applied to transfer the toner particles to the receiver member in the image-wise pattern to form the desired print image on the receiver member. The receiver member is then removed from its operative association with the dielectric member and subjected to heat and/or pressure to permanently fix (typically referred to as fusing) the toner particle print image to the receiver member. Plural toner particle images of, for example, different color particles respectively can be overlaid in the above manner on the receiver member before fusing to form a multi-color print image.
In the earlier days of electrophotographic printing, the toner particles were relatively large (e.g., on the order of 10-15 μm. As a result the print image had a tendency to exhibit an unwanted and not reproducible weak relief appearance (variably raised surface). Under most circumstances, the relief appearance was considered an objectionable artifact in the print image. In order to improve image quality, and to reduce relief appearance, over the years, smaller marking particles (e.g., on the order of less than 8 μm have been formulated and are more commonly used today. In order to achieve higher resolutions and to reduce toner consumption there is a tendency to reduce the size of the marking particles even more.
With the improved print image quality, print providers and customers alike have been looking at ways to expand the use of electrophotographically produced prints. In certain classes of printing, a tactile feel to the print, is not objected to, in particular, when the tactile feel can be controlled by providing raised information at selected regions only. Such raised information can be used to authenticate certain print products by tactile feel. If such print products are attached to or accompany a particular product, the print product may provide valuable information with respect to authenticity of the product itself.
Product counterfeiting occurs on a multitude of products such as artworks, CDs, DVDs, computer software recorded on CDs or diskettes, perfumes, designer clothes, handbags, briefcases, automobile and airplane parts, securities (e.g. stock certificates), identification cards (driver's licenses, passports, visas, green cards), credit cards, smart cards, and pharmaceuticals. According to the World Health Organization, a substantial percentage of the world's pharmaceuticals is bogus and may indeed be detrimental to the patient consuming the same. Thus there is a need to authenticate products.
The application of security markers to a object or product for authenticating the origin and intended market of the object product are known in the prior art. Such security markers can be incorporated into components which make up the object or can be incorporated into papers, inks, or varnishes that are applied to the object or into labels affixed to the object or packaging for the object. The presence of such security markers verifies the authentic origin of the object and is verified by means suited to the particular nature of the marker. Examples for such security markers are RFID-tags and holograms.
Both of these markers can be detected by non-destructive non contact methods. For example, authentication devices can be used which detect the electronic or optical properties of the markers, in situ, without the need to alter or destroy the object on which they reside. As such they provide means for authenticating a product. However, the costs associated with both markers are relatively high and thus are not widely used for high volume, low cost applications.
Using a raised print, which provides a tactile feel, as discussed above, also provides a means for authenticating a print product and thus possibly another product accompanying the same, albeit at a much lower cost. The tactile feel or the lack thereof can be easily recognized by the end user. Providing a tactile feel alone to authenticate a product, however, may not be sufficiently reliable, especially in an automated environment.